The present invention relates in general to testing of integrated circuits, and in particular to method and apparatus for testing of integrated circuits at temperatures other than ambient temperature using Peltier type devices.
Integrated circuits (ICs) are typically designed to be fully operational within a specified range of temperatures. In some applications this range is wide enough to test the limits of the various technologies involved. The need to operate an IC at temperatures as low as -30.degree. C. or -40 .degree. C., for example, often leads to additional complication and expense at the testing stage. Traditionally devices are pre-cooled and fed into a cold chamber surrounding the test head. The test chamber and test heads are maintained at the low temperature using liquid Nitrogen as a heat sink. This method suffers from a number of drawbacks. It requires plumbing low temperature liquid Nitrogen which needs careful controls because of the danger associated with liquid Nitrogen. This type of temperature control method also demands measuring the temperature of a large thermal mass which can be costlier and tends to compromise accuracy. Condensation, and in some instances ice formation, on the surfaces and test heads is also a source of potential problems whereby mechanical systems are disrupted, and electrical contacts are rendered high impedance or intermittent. To avoid inaccurate temperature control and unreliable test results additional provisions for controlling the atmosphere around the test device are required to reduce or eliminate condensation. Further, when an IC is brought into contact with the test head, care must be taken to limit the perturbation effect on the temperature of the low thermal mass IC caused by the temperature of the test head. These and other types of problems exist when the IC is to be tested at temperatures significantly higher than the ambient temperature. The high or low temperature testing can be made further complicated by the type of circuitry that is integrated on the IC. For example, certain ICs include magnetic sensitive devices (e.g., Hall-effect devices) that create additional problems associated with generating the magnetic fields using an electromagnet at the various temperatures.
There is therefore a need for a low mass test system with an accurate temperature control and a limited surface area for temperature testing.